Package fof cooking foodstuffs having high-moisture content

ABSTRACT

A package for cooking includes an inner ply and an outer ply laminated to the inner ply. The inner ply contact foodstuffs contained within the package. The inner ply is a paper-based product having a wet tensile strength property such that it will not deteriorate in the presence of high-moisture foods. The paper-based product also has a scorching temperature above the temperature of the foodstuffs when heated. The outer ply includes a polymer film.

TECHNICAL FIELD

The present invention relates to packaging. More specifically, the present invention relates to a laminated package usable in microwave cooking applications.

BACKGROUND OF THE INVENTION

While once relegated to heating up leftovers and popping an occasional bag of popcorn, microwaves have now become a cooking staple in many homes. Whether making an entire meal or zapping a side dish, microwaves provide a quick and easy alternative to conventional cooking methods.

Although generally quicker and easier than conventional cooking, microwave cooking is not without its drawbacks. Microwaves tend to dry out food that should be moist and tend to soften foods that should be crisp. As a result, some flavor and appeal may be lost when cooking in the microwave. Moreover, the microwave product may lose some of the nutritional value of its conventionally cooked counterpart.

To combat the above-described problems associated with microwave cooking, several products and methods have been tried. For example a number of packages have become available that are designed for microwave cooking. In most applications, the packaging is relatively standard packaging for a frozen product, i.e., it is designed to be stored in the freezer with foodstuffs therein, but can then be transferred to the microwave for cooking. Such packages consist of a thermoplastic laminate having multiple layers of thermoplastic materials.

In the conventional packaging, foodstuffs contained within the package contact one of the thermoplastic layers. However, when certain products are prepared in these conventional packages, particularly products having high moisture content and/or having sauces or spices included for flavoring, the heated-up products contacting the thermoplastic deform the thermoplastic. This deformation may be manifested as scorch-marks, marring, bubbling, charring or the like. This deformation of the thermoplastic may or may not create a food contamination problem, but at the very least, the visual effect of the bubbled, melted plastic is unappealing to a user. In fact some users assume the product is bad based on the visual deformities and may refuse to eat the product, or worse, refuse to again buy the product.

Accordingly, there is a need in the art for an improved package designed for microwave cooking. There is a need in the art for a package in which foodstuffs can be frozen and subsequently cooked in a microwave. There also is a need in the art for a microwave cooking package that effectively cooks the foodstuffs contained therein without damaging the foodstuffs or the package.

SUMMARY OF THE INVENTION

The present invention addresses the foregoing needs in the art by providing an improved package for microwave cooking. It is also contemplated that the packaging could be used in other types of cooking, for example, cooking in a conventional oven

In one aspect of the present invention, a package includes an inner ply and an outer ply laminated to the inner ply. The inner ply contact foodstuffs contained within the package. The inner ply is a paper-based product having a wet tensile strength property such that it will not deteriorate in the presence of high-moisture foods. The paper-based product also has a scorching temperature above the temperature of the foodstuffs when heated. The outer ply includes a polymer film.

In another aspect, a multi-layer package for use in cooking foodstuffs includes an inner ply, an outer ply, and a vent. The inner ply contacts the foodstuffs and is a paper-based product having a scorching temperature above a maximum temperature reached by the foodstuffs during microwave heating of the foodstuffs. The outer ply is laminated to the inner ply and is a polymer film. The vent is disposed in the pressure to relieve pressure within the package during microwave cooking.

These and other aspects and objects of the invention will be apparent from the following description and attached figures, in which preferred embodiments of the present invention are described and depicted.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1A is a representation of a conventional known microwave package.

FIG. 1B is a sectional view of the area indicated 1B in FIG. 1A.

FIG. 2A is a perspective view of a microwave cooking package according to a preferred embodiment of the present invention.

FIG. 2B is a cross-sectional view of the microwave cooking package of FIG. 2A taken along sectional line 2B.

FIG. 3 is a cross-sectional view of a microwave cooking package according to another embodiment of the present invention.

FIG. 4 is a table showing experimental test results for cooking packages made in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As described above, many commercial packaging products used for storing and subsequently microwaving food products are known. A conventional package 10 is illustrated in FIGS. 1A and 1B. Generally, a conventional package 10 has a multi-ply construction in which an inner ply 12, i.e., a ply that contacts the product contained within the package, is a thermoplastic. An outer ply 12 laminated to the inner ply 10 also is conventionally a thermoplastic material on which instructions, branding, and the like can be printed. When certain foods are heated in this conventional package, the inner ply contacting the food often becomes deformed.

An improved microwave-cooking package 20 according to a first embodiment of the invention is illustrated in FIGS. 2A and 2B. Similar to the conventional packaging, the package 20 has a multi-ply construction. Specifically, an inner ply 22 is disposed for contacting foodstuffs contained within the package and an outer ply 24 is disposed on a side of the inner ply 22 opposite the foodstuffs. The inner ply 22 and the outer ply 24 preferably are laminated to each other.

The inner ply 22 preferably is a paper-based layer and the outer ply 24 preferably is a polymer film or a thermoplastic. The paper-based product used to form the inner ply preferably is one of Kraft paper, bleached Kraft paper, parchment paper, greaseproof paper, glassine paper, rice paper, or cellophane. Although not limiting to this disclosure, the inventor has conducted tests with the following commercially available papers: Reynolds parchment 10900-01331, Fox River WOGR, and Wausau Nos. GG 243W00, GN404838, GF323182, GF235174, GN214933, and GF205204.

Preferably, the paper product comprising the inner ply 22 has a wet tensile strength between about 10% and about 50%. More preferably, the wet tensile strength of the inner ply is between about 20% and about 30%. The inventor has found that when the inner ply is formed of a paper product having a wet tensile strength that is less than about 10%, the package will deteriorate, particularly when higher moisture foods, namely foods having a moisture content of between about 65% and about 85% are contained in the package. Preferably, the package of the invention can be used with foods having moisture contents in this range, and more preferably with foods in the range of about 70% to about 75% moisture content. Paper products having higher wet tensile strength products also can be used, although such paper products tend to be more expensive.

The paper-based product comprising the inner layer 22 preferably also is characterized in that it has a scorching temperature that is above a maximum temperature the foodstuffs contained within the package will reach during cooking. Accordingly, burning or charring of the inner ply 12 will not occur when the package is heated in the microwave. Preferably, the scorching temperature of the inner layer is above about 290° F.

The package 20 according to the foregoing description is particularly well-suited for use with foodstuffs having high-moisture content resulting from their inclusion of sauces or excess water used for steaming the product. As a result of their high-moisture content, when the products contained within the package 20 are heated, steam is created that inflates the package. The package according to the present invention preferably includes a venting mechanism that allows the steam to be exhausted before the package becomes deformed or, in an extreme case, explodes.

In one example, venting is partially accomplished by virtue of the characteristics of the inner ply. Specifically, the porosity of the paper product comprising the inner ply is such that the steam generated in the package can escape through the pores in the paper. For example, paper products having a porosity of between about 29 and about 15,000 sec/100 ml are believed to be effective in such an embodiment. Once through the paper-based inner ply, the steam preferably is then vented out an opening formed between the inner ply and the outer ply or through the outer ply.

FIGS. 2A and 2B illustrate one preferred embodiment in which the steam vented through the pores in the inner ply is subsequently vented from the package between the inner ply and the outer ply. Specifically, a channel 26 is formed between the inner ply 22 and the outer ply 24. The channel 26 preferably is formed by de-laminating a portion between the inner ply 22 and the outer ply 24. In one embodiment, the channel 26 is formed by omitting the adhesive used to laminate the first and second plies. The channel preferably terminates at an outlet 28, which is open to the atmosphere. The outlet may be disposed at an edge of the package, or may be in any other position on the package. Thus, in this embodiment, steam exhausts through the pores of the inner ply 10, enters the channel 20 and escapes the package through the opening 22. In another embodiment, the channel 20 could have more than one outlet, for example, on opposite ends of the package. In this embodiment, the channel could extend substantially along either or both of a length and width of the package.

The outlet may be always open to the atmosphere, or it may be selectively opened. For instance, the outlet 28 may include a seal that is sealed until some event occurs to open or break the seal. The seal may be resealable, or it may be a single-use seal. In one preferred embodiment, the seal is pressure activated such that when sufficient pressure builds up behind the seal, the seal will open and allow excess steam to escape. In this manner, the venting mechanism acts as a bleed valve behind which a relatively large amount of pressure must build up before any of the pressure is bled off. When minimal steam is desired in the package, the seal may open at a relatively low pressure, whereas when it is desirable to maintain an amount of the steam in the package during cooking, for example, to steam the contents of the package, the seal opens at a relatively higher pressure.

The seal comprising the outlet may be formed in a number of ways. For instance, the seal may be formed by including a one-way valve at the outlet which allows steam to exhaust. In another embodiment, an adhesive is used that creates a temporary bond between the inner ply and the outer ply at the outlet. The bond is temporary in that a sufficient force, i.e., resulting from an elevated pressure, in the channel upstream of the bond will overcome the adhering force of the adhesive, thus causing the bond to break. The inner ply and the outer ply thus separate and steam exhausts. The bond preferably is sufficiently strong that the bond is sealed at all times other than cooking, for example, to prevent leaking from the package and/or to prevent contaminants from entering the package.

In another embodiment, a temporary bond also may be formed to close the channel, but the bond in this embodiment comprises a heat seal that is broken at a predetermined temperature obtained by the package and/or the contents within the package, i.e., a predetermined venting temperature. Specifically, the outlet includes a heat seal that melts or de-adheres when the package and/or the contents of the package reach the venting temperature. The heat seal may consist of a pattern in which the adhesive between the inner and outer plies is arranged. The heat seal could comprise more than just the outlet 28. In fact, the heat seal could form any or all of the channel 26. As will be understood, steam will only pass through the heat-sealed portion of the package when a sufficient temperature is reached to open the heat seal.

In the embodiments described above, steam passes through the inner ply of the laminate packaging material through pores inherent in the inner ply. Alternatively, the inner ply may be perforated or otherwise manufactured to include pores, for example, micropores. In another embodiment, a slit or similar opening may be formed through the inner ply in communication with the channel 26.

In yet another embodiment of the invention, the porosity of the paper is sufficiently low that steam will not permeate the paper. In this embodiment, a different venting mechanism preferably is provided that selectively allows and prohibits passage of steam there through, i.e., to selectively vent steam from or retain steam in the package. An exemplary configuration of this embodiment is illustrated in FIG. 3. As depicted therein, a heat seal 36 is provided between opposing inner plies 32 that define the space in which foodstuffs are contained. Outer, polymer plies 34 are laminated to a side of the inner plies opposite the side contacting the foodstuffs. In this embodiment, the heat seal 36 is broken when the temperature within the package reaches a venting temperature. The heat seal in this embodiment is similar to the heat seal described above, except that instead of being formed between the plies comprising the laminate material, i.e., between the inner and outer plies, the heat seal preferably is formed between separate laminate layers. The heat seal illustrated in FIG. 3 is formed at a seam of the package. More particularly, the heat seal comprises some or all of the adhesive used to secure opposite sides of the package to each other or used to close the package after filling. When this preferred package is heated in the microwave, the adhesive melts and the pressure within the package separates the previously-sealed opposing inner plies, thus allowing the package to vent. In other embodiments, the heat seal may be formed at some other position on the package. In these other embodiments, an aperture or the like is provided through the inner ply through which steam can be exhausted.

In yet another embodiment of the invention, instead of using a channel through which steam escapes to an outlet, an aperture may be formed directly through all plies comprising the package, and steam is allowed to vent through this aperture. The aperture may be completely open during cooking, for example, a tab could be applied to cover the whole prior to use, which tab is removed by a user prior to cooking. Alternatively, the aperture may uncover during the cooking process. For example, a cover may cover the aperture by virtue of a heat sensitive adhesive that melts during cooking. The melting of the adhesive combined with the pressure within the container forces the aperture to become uncovered, thereby venting the package.

Any number of adhesives may be used to seal the package, to laminate the layers, and/or to create the destructible heat seal. Specifically, the invention contemplates the use of water-based, solvent-based, hot melt, and solventless adhesives Some commercial adhesives tested by the inventor include H. B. Fuller WC 3460 ZZ; H. B. Fuller PWF-3007; Royal 20394; Royal 20123; Hycar 26288; Hycar 26315; Dow Primacor 5986, 5990, 59801, and 59901; and Dow Hypod™ DPOD 4501 and 8501. As should be appreciated, any adhesive that could contact the food stuffs contained within the package should preferably be safe for human consumption.

As described above, the preferred package according to the invention is formed by laminating two layers or plies. The lamination preferably is maintained using an adhesive. Solvent-based, solvent-free, and water-based adhesives are known in the art, and may be used to bond the plies 12, 14. The inventors have found, however, that water-based adhesives may be less desirable when the product contained in the package has a relatively high moisture content, as the water-based adhesives tend to re-liquefy during heating, thus resulting in delamination of the plies. The above-mentioned adhesives also may be used to form the vents and/or heat seals described above.

As noted above, the outer ply preferably is a polymer film. Such films are generally preferred for the outer ply because their appearance, especially when printed on, is preferable. As described above, the polymer film preferably is laminated to the inner, paper ply. The polymer film may be an oriented polyester (OPET) film, such as DuPont Mylar 813/48 gauge, EB 11/48 gauge, or 822/48 gauge. Alternatively, the polymer film may be an oriented polypropylene (OPP) film such as AET films AQS/70 gauge. Of course, one of the ordinary skill may appreciate that other polymer films could be used, including other OPET and OPP films, and films other than OPET and OPP.

The invention is not limited to packages having two plies. It is anticipated that additional plies also may be used. Moreover, one or more plies used in the preferred microwave package may be coated, for example, to aid in lamination and/or to provide a barrier layer. When adhesives are used either during formation of the package, such a barrier layer may be required to ensure that the adhesives cannot contact the foodstuffs, for example, because the adhesives are not FDA-approved.

Although the invention is described as having an inner, paper ply and an outer polymer ply, both plies could be made of paper. By eliminating the polymer ply, the package may be more environmentally-friendly. Using biodegradable adhesive also may be desirable. The package also may include only a single ply. For example, the single ply would be the inner, paper ply. In this arrangement, the inner ply preferably would be at least partially coated with an adhesive that would facilitate formation of the single ply into a package or a pouch. The adhesive preferably would be heat-sensitive and would melt at a predetermined temperature to vent the container, or alternative venting mechanisms, such as those described above, could be used.

FIG. 4 illustrates a number of clinical trials for various paper/adhesive/polymer combinations.

The foregoing embodiments of the invention are representative embodiments, and are provided for illustrative purposes. The embodiments are not intended to limit the scope of the invention. Variations and modifications are apparent from a reading of the preceding description and are included within the scope of the invention. The invention is intended to be limited only by the scope of the accompanying claims. 

1. A package comprising: an inner ply that contacts foodstuffs contained within the package, the inner ply comprised of a paper-based product having a wet tensile strength property such that the paper-based product will not deteriorate in the presence of high-moisture foods and having a scorching temperature above the temperature of the foodstuffs when heated; an outer ply disposed on the inner ply, the outer ply comprising a polymer film.
 2. The package of claim 1, wherein the paper has a wet strength property of from about 10% to about 60%.
 3. The package of claim 1, wherein the paper has a wet strength property of from about 20% to about 35%.
 4. The package of claim 1, further comprising a vent disposed for releasing pressure from within the package to the atmosphere.
 5. The package of claim 4, wherein the vent is a channel formed between the inner ply and the outer ply and being open to the atmosphere.
 6. The package according to claim 5, wherein the channel is formed by de-laminating a region between the inner ply and the outer ply.
 7. The package of claim 4, wherein the vent is opened when the pressure within the package reaches a predetermined pressure.
 8. The package of claim 4, wherein the vent comprises a seal that is selectively opened to relieve pressure within the package.
 9. The package of claim 8, wherein the seal comprises an adhesive that at least partially de-adheres in the presence of one or both of increased temperature and pressure and therefore opens the vent at a predetermined venting condition.
 10. The package of claim 8, wherein the seal is opened when the interior of the package reaches a predetermined pressure.
 11. The package of claim 10, wherein the seal comprises a flap disposed over an aperture formed through the inner layer and the outer layer.
 12. The package of claim 1, wherein the paper product is one of Kraft paper, bleached Kraft paper, parchment paper, greaseproof paper, and glassine paper.
 13. The package of claim 1, wherein at least one of the inner ply and the outer ply is coated with a material forming a barrier layer.
 14. The package of claim 13, further comprising an adhesive provided on one of the barrier layer and the outer ply, the adhesive being used for at least one of sealing the package, laminating the plies of the package, and forming a temporary seal in the package.
 15. The package of claim 4, wherein the vent comprises at least one aperture formed through the inner layer.
 16. The package of claim 15, wherein the vent further comprises a channel between the inner layer and the outer layer being open to the atmosphere and in communication with the at least one aperture, such that pressurized air exiting the package through the at least one aperture is exhausted from the package through the channel.
 17. The package of claim 15, wherein the at least one aperture comprises a plurality of micropores.
 18. The package of claim 17, wherein the micropores also are formed through the outer layer.
 19. The package of claim 4, wherein the vent comprises a selectively coverable aperture formed through the inner and outer plies of the package.
 20. A multi-layer package for use in cooking foodstuffs, the package comprising: an inner ply contacting the foodstuffs, the inner ply comprised of a paper-based product having a scorching temperature that is higher than a maximum temperature of the foodstuffs reached during cooking of the foodstuffs; an outer surface facing the environment and comprising a polymer film; and a vent disposed in the package for relieving pressure within the package during cooking.
 21. The package of claim 20, wherein the paper product comprising the inner ply has a wet tensile strength property such that the inner ply will not deteriorate in the presence of high-moisture foods.
 22. A package for cooking foodstuffs comprising: a single ply contacting the foodstuffs, the single ply comprised of a paper-based product having a scorching temperature that is higher than a maximum temperature of the foodstuffs reached during cooking of the foodstuffs; and an adhesive sealing the single ply to form the package, the adhesive having a melting point at a temperature reached during cooking such that the seal is melted during cooking to vent the package. 